The energy equivalent of NADH is 3 ATP molecules. NADH is a coenzyme that plays a critical role in cellular respiration, specifically in the process of oxidative phosphorylation.

Oxidative phosphorylation is the final stage of cellular respiration and occurs in the inner mitochondrial membrane. During this process, the high-energy electrons carried by NADH are transferred to the electron transport chain, which consists of a series of protein complexes embedded in the mitochondrial membrane.

The transfer of electrons through the electron transport chain leads to the pumping of protons (H+) from the mitochondrial matrix to the intermembrane space, creating an electrochemical gradient. This gradient drives the synthesis of ATP through ATP synthase, a protein complex located in the inner mitochondrial membrane.

The energy released from the transfer of electrons is used to pump protons, and this energy is ultimately harnessed to produce ATP. The exact number of ATP molecules generated per NADH molecule depends on the efficiency of the electron transport chain and ATP synthase.

According to experimental data, it is estimated that the transfer of 2 electrons from NADH through the electron transport chain leads to the synthesis of approximately 3 ATP molecules. This is because the electron transport chain is coupled to the movement of protons across the inner mitochondrial membrane. For every 2 electrons transferred, it is believed that 10 protons are pumped, which is sufficient to produce 3 ATP molecules through ATP synthase.

It is important to note that the energy yield from NADH is higher than that of FADH2, another coenzyme involved in cellular respiration. This is because NADH enters the electron transport chain at a higher energy level and can donate its electrons earlier, resulting in the pumping of more protons and the synthesis of more ATP.

In conclusion, the energy equivalent of NADH is 3 ATP molecules. NADH plays a crucial role in cellular respiration by transferring high-energy electrons to the electron transport chain, leading to the synthesis of ATP through oxidative phosphorylation.